With the rapid popularization of urban rail transit and the significant increase in vehicle speed, higher design and use requirements have been proposed for the beam structures (sleeper beam and towing beam) that constitute the main components of the vehicle body.
The beam structure applied to the rail vehicle is a key component for connecting and carrying the vehicle body and the bogie, and is also a main component for the driving force transmission between the vehicle body and the bogie. Among the existing rail vehicles, taking the subway vehicle as an example, the stainless steel body of the subway vehicle is basically made of austenitic stainless steel material, and only the towing beam structure and the sleeper beam structure are still made of thick plate of carbon steel material. After years of continuous research and improvement, the light-weighting of this type of vehicle body has basically reached the limit. Since the strength of the stainless steel material is higher than that of the ordinary carbon steel material, the development and design of the stainless steel beam structure can significantly reduce the thickness of the plate, thereby achieving the purpose of further reducing the weight of the vehicle body. At the same time, because stainless steel has good corrosion resistance, replacing the traditional carbon steel beam structure with stainless steel beam structure can reduce the manufacturing and maintenance cost of the stainless steel vehicle body without coating process.
However, due to the low thermal conductivity of the stainless steel material, the traditional electric-arc welding method is prone to generate large residual stress and deformation when welding the stainless steel structure. Therefore, when the stainless steel material is used to simply replace the beam structure of the existing carbon steel material, the dimensional requirements of the structural members cannot be guaranteed, and the later service safety (such as stress corrosion performance) thereof is also adversely affected due to the large amount of welding, severe structural deformation and residual stress. Therefore, for the stainless steel beam structural member, in order to reduce the welding deformation and improve the welding quality, the welding method with heat source of high energy density such as laser welding or electron beam welding is preferably to be used.
The laser welding has the advantages of deeper fusion penetration, high efficiency, low welding deformation and stress. However, this method requires rigorous assembly precision of structural members, and it has great difficulties in engineering application from the perspective of welding manufacturing. Electron beam welding requires vacuum environment, it is difficult to weld the large and complex structures. Therefore, in order to replace the carbon steel beam structure with the stainless steel material, new ideas and methods in structure and process need to be proposed.